The function of the jaw crusher is based on the force pressing stone, the jaw moving in respect of an eccentric shaft moves back and forth regarding the fixed jaw. Movable jaws i.e. pitmans of the jaw crushers have been produced in various different ways. A casted pitman is enclosed i.e. closed in its cross-sectional profile. In the patent publication EP1049539B1, there is presented a jaw crusher with a pitman with closed cross-sectional profile.
Manufacturing a pitman according to a closed profile requires several different work phases. When casting, cores are needed for manufacturing closed profile parts. The moving of cores during casting has lead to differences in wall thicknesses of the webs, because of which the wall thickness of the castings have to be oversized, which adds to the cost and dynamic forces. It is difficult to check and correct casting and quality errors in an enclosed pitman. In an enclosed structured pitman, various exhaust openings are needed for removing the sand in the core. Sand removal through exhaust openings after the casting is laborious and time consuming.
In known solutions, for reaching sufficient strength plenty of material is required in the lower part of the pitman. This increases the mass of the pitman, which increases dynamic forces.
When the material to be crushed is located one-sidedly in the crushing chamber it is a question of one-sided crushing. In that case, momentary transformations are developed in the pitman due to the one-sided strain, which transformations distort the pitman. The transformations increase power requirement and reduce crushing capacity. Additionally, the material in the pitman is exposed to fatigue, especially in the area of the supporting point of the toggle plate.
In some cases, the side plates of the body of the jaw crusher are joined with each other by an intermediate rod in the part between the ends of the body. A typical location for the intermediate rod is in the location of the pitman. A horizontal hole for the intermediate rod leading from the first side of the body to the second side of the body is formed in the pitman because of this. In the casting process, a core is placed in the hole for the intermediate rod, the sand of which core has to be removed after casting. In cooling down, thermal stresses result in the hole for the intermediate rod that do not necessarily entirely disappear in the thermal treatment. It is known that the hole for the intermediate rod is non-machined and the hole with cast surface is sensitive to crack formation. The area of the hole for the intermediate rod is a critical spot because of the peak stresses caused by the crushing force.